This application claims priority to PCT Application Serial No. PCT/US2006/039808, filed on Oct. 12, 2006.
This invention relates to a turbofan engine, and more particularly, the invention relates to managing the operational line of a low pressure compressor.
A typical turbofan engine includes low and high spools. The low spool is coupled to a turbofan and typically supports a low pressure turbine and low pressure compressor. The high spool rotates relative to the low spool and typically supports a high pressure compressor downstream of the low pressure compressor and is coupled to a high pressure turbine upstream of the low pressure turbine. The spools, turbine and compressor are housed in a core nacelle. The turbofan is arranged upstream from the core nacelle. A fan nacelle surrounds the turbofan and core nacelle to provide a bypass flow path.
Maintaining aerodynamic stability of the low pressure compressor is a significant factor for overall engine performance, in particular for large commercial high bypass flow engines. The low pressure compressor operating characteristics are set to maintain a sufficient stability margin for the compressor at all operating conditions, including throttle transients. A limitation on the stability margin is an increase in low pressure compressor pressure ratio that occurs during throttle transients. During a deceleration, the high spool pressurizes the low pressure compressor while the turbofan and low pressure compressor depressurize. This results in a momentary increase in the low pressure compressor pressure ratio, which raises the low pressure compressor operating line and reduces stability margin until the high spool decelerates.
Typically, the nominal low pressure compressor operating line is set such that sufficient stability margin is maintained during deceleration throttle transients. This can result in the low pressure compressor being operated at non-optimal performance conditions. What is needed is a turbofan engine that maintains a desired operating line for the low pressure compressor that maximizes performance and ensures sufficient stability margin for throttle transients throughout the flight envelope.